A file descriptor is simply a number that the operating system assigns to an open file to keep track of it. Caddy’s primary goal is to be an easy-to-use static file web server. Having high file descriptor limit means it can open more files to serve users at the same time.

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$ ulimit -Sn && ulimit -Hn

1024

4096

The current system is too low in both soft and hard limits. But since it’s not in production, warning can be ignored.

Make sure the server working:

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$ http :2015

HTTP/1.1404Not Found

Content-Length: 14

Content-Type: text/plain; charset=utf-8

Server: Caddy

X-Content-Type-Options: nosniff

404Not Found

Response header X-Content-Type-Options: nosniff prevents MIME based attacks, it tells the browser to respect the response content type, not to override.